I'm going to ignore point (1) because as far as I'm concerned, Stack Overflow has already proven you wrong. Or at least it proves that "difficult" is not equivalent to "impossible" if you do it right.
Point (2) is interesting, but also incorrect. The core audience for Stack Overflow came from the combined readership of various blogs, which you quietly ignore. People blog about other subjects too. All it takes is a few of those bloggers to drop names, and you're in.
Point (3) is slightly more reasonable, and it's fully addressed by the entire Area 51 proposal process as well as community and official moderation on the betas. You may not have noticed it, but people actually are out there, asking good questions; positioning the site toward experts is simply a matter of weeding out the really poor ones.
Point (4) is wrong again. SE sites will probably have ads, just not in the beginning (when the team was asked, the official response was something along the lines of "not yet"). And since you haven't defined "success" or "failure" at all, I'm going to define the former as "breaking even" on the bandwidth and hosting costs. I'm not an insider, but the team has blogged several times about what it takes to run Stack Overflow, and it's not monstrous; many SE sites can probably be hosted on a single server while they're small, so it won't take all that much to recoup any losses.
Of course I can't know that SE will be a smashing success; no one can. But obviously the venture capitalists pouring money in believe it, as does the team and as do the thousands of users participating in the various betas. What I can say for sure is that your "evidence" for SE's inevitable failure is suspect at best, and your argument is... a fail. The points you're making are, quite frankly, blindingly obvious, and apply equally well to any new business; no matter what you're doing, you have to to recruit the best "employees", build up a customer base, and tighten up the financials as much as possible so that you're actually turning a profit. SE really isn't any different.
Starting a business is hard. Running it is harder. Just because it looks like it's too hard to you, doesn't mean that people who are much more experienced and have a lot more money to burn will fail.